I hate him. I'm 15 and overwhelmed with rage because of my mother's husband. He's a chain-smoking alcoholic who brawls in the streets and can't say a single sentience without adding "ya know". He's a wantabe hell's-angle and a wantabe buddhist.
And for some reason he hangs up portraits of Jesus all over the house even though he knows were all athiests. He's really short, hugely over weight and has a face like old discarded leather.
He's always trying to put me down by saying things like "Don't you think your pathetic because you've never had a boy-friend(ya know)" and when I was talking to my brother's girl-friend about global-warming and the ozone layer is being destroyed, he butted in and said that humans made the ozone layer better and that scientist had made a mistake.
I could of said any thing and he'd disprove it. He thinks he's the master of the house because he's the man even though he's unemployed and lets my mother do all the work (i.e. bring in the money, do the shopping, cook the food and clean the house),
he's also the world's biggest misogynistic and says that no women, no matter how great, can be better than a man at any thing (by his logic some drunkard down at the pub would have made a better Joan of Ark).
But the worst part is that my bedroom is under their's and I can hear all they're "going on's".

Does anyone have any advice for me to deal with him before he starts getting physically abusive?

Have you talked to your mom at all? Have they been married for just a short time? Your description of him is pretty bad, but I understand that there is alot of anger in there for you. Does it have something to do with your father being out of the house? Would it be possible to move in with your father?
At 15, everything seems so magnified whether they are good or bad. That is not to discount what you are feeling at all. Of course your feelings and opinions are valid, you have to live with it. But understand that there is such a short time till you will have a bit more freedom, and be able to get away from the situation more.
Talk to your mom, better yet, show her the post you wrote....don't underestimate her ability to help the situation.